If you owned stock in a company that went bankrupt and the stock became worthless, enter it as a sale of stock in the Stock, Mutual Funds, Bonds & Other interview of Federal Taxes > Wages & Income > Investment Income.

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Don't own stock, it was a start up company.

No.

Enter it in the investment sales (disposition) section of TurboTax.

When you sell stocks, bonds, mutual funds, or other securities, you should get Form 1099-B.  

But what about non-security investment sales like coins, collectibles, timber, land, or a second home? Here's how you enter those:

1. Open (continue) your return in TurboTax.
2. In the search box, search for investment sales then select the Jump to link in the search results.
3. Answer Yes to the question Did you sell stocks, mutual funds, bonds,  or other investments in 2019?
   • If you land on the Here's the investment sales we have so far screen, select Add More Sales.
4. Answer No to the 1099-B question.
5. On the next screen, select the type of sale you had (like second home, collectible, or land) and Continue.
6. Continue following the onscreen instructions to enter the sale.

Source: TurboTax FAQ

no